This invention is generally directed to toner compositions, and more specifically, the present invention relates to toner polymers with low fuser set temperature and broad fusing latitude obtained by the crosslinking of low molecular weight copolymers like styrene-1,2-butadiene copolymers. In one embodiment, the present invention is directed to toner polymers prepared by the crosslinking of styrene-1,2-butadiene copolymers in an extruder, and the preparation of toners thereof, and wherein the toner characteristics may be modified by the addition of certain components like hexafluoroacetone. More specifically, in one embodiment of the present invention there are provided developer compositions formulated by admixing toner compositions containing the toner polymeric resins prepared as illustrated herein, and carrier components. In one specific embodiment of the present invention, there are provided toner compositions with copolymers prepared by extrusion, which polymers are nontoxic, nonblocking at temperatures of less than 50.degree. C., for example, easily jettable, melt fusable with a broad fusing temperature latitude, cohesive above the melting point of the resin, and triboelectrically chargeable. Moreover, in addition the toner compositions of the present invention possess low fusing temperatures, and therefore, lower fusing energies are required for fixing enabling less power consumption during fusing, and permitting extended lifetimes for the fuser systems selected. Accordingly, the toners of the present invention can be fused (fuser roll set temperature) at temperatures of 260.degree. F. or less as compared to many currently commercially available toners which fuse at temperatures of from about 300.degree. to about 325.degree. F. With further respect to the present invention, the extrusion prepared polymers selected have a T.sub.g-mid of from between about 26.degree. to about 60.degree. C., and preferably from about 40.degree. to about 58.degree. C. as determined by DSC and by other known methods. Also, the toner and developer compositions of the present invention are particularly useful in electrophotographic imaging and printing systems, especially xerographic imaging processes.
The electrostatographic process, and particularly the xerographic process, is well known. This process involves the formation of an electrostatic latent image on a photoreceptor, followed by development, and subsequent transfer of the image to a suitable substrate. Numerous different types of xerographic imaging processes are known wherein, for example, insulative developer particles or conductive toner compositions are selected depending on the development systems used. Moreover, of importance with respect to the aforementioned developer compositions is the appropriate triboelectric charging values associated therewith as it is these values that enable continued constant developed images of high quality and excellent resolution; and admixing characteristics. Specifically, thus toner and developer compositions are known, wherein there are selected as the toner resin styrene acrylates, styrene methacrylates, and certain styrene-1,4-butadienes, including those available as PLIOLITES.RTM.. Other resins, including certain crosslinked resins, U.S. Pat. No. Re. 31,072, and polyesters as illustrated in U.S. Pat. No. 3,590,000 have also been selected for incorporation into toner compositions. Moreover, it is known that single component magnetic toners can be formulated with styrene-1,4-butadiene resins, particularly those resins available as PLIOLITE.RTM.. In addition, positively charged toner compositions containing various resins inclusive of certain styrene-1,4-butadienes and charge enhancing additives are known. For example, there are described in U.S. Pat. No. 4,560,635, the disclosure of which is totally incorporated herein by reference, positively charged toner compositions with distearyl dimethyl ammonium methyl sulfate charge enhancing additives. This '635 patent also illustrates the utilization of suspension polymerized styrene-1,4-butadienes for incorporation into toner compositions, reference for example working Example IX.
Numerous patents are in existance that illustrate toner compositions with various types of toner resins including, for example, U.S. Pat. Nos. 4,104,066, polycaprolactones; 3,547,822, polyesters; 4,049,447, polyesters; 4,007,293, polyvinyl pyridine-polyurethane; 3,967,962, polyhexamethylene sebaccate; 4,314,931, polymethyl methacrylate; U.S. Pat. No. 25,136, polystyrenes; and U.S. Pat. No. 4,469,770, styrene-1,4-butadiene copolymers.
Disclosed in U.S. Pat. No. 4,529,680 are magnetic toners for pressure fixation containing methyl-1-pentene as the main component. More specifically, there are illustrated in this patent, reference column 2, beginning at line 66, magnetic toners with polymers containing essentially methyl-1-pentene as the main component, which polymer may be a homopolymer or copolymer with other alpha-olefin components. It is also indicated in column 3, beginning at around line 14, that the intrinsic viscosity of the polymer is of a specific range, and further that the melting point of the polymer is in a range of 150.degree. to 240.degree. C., and preferably 180.degree. to 230.degree. C.
Additionally, there are specifically illustrated in U.S. Pat. No. 4,558,108 toner compositions with suspension polymerized styrene-1,4-butadienes, aforementioned resins, pigment particles, and charge enhancing additives.
In addition, several recently issued patents illustrate toner resins including vinyl polymers, diolefins, and the like, reference for example U.S. Pat. No. 4,560,635. Moreover, there are illustrated in U.S. Pat. No. 4,469,770 toner and developer compositions wherein there are incorporated into the toner styrene-1,4-butadiene resins prepared by emulsion polymerization processes.
Illustrated in U.S. Pat. No. 4,952,477 (Aug. 28, 1990) are low melting toners with semicrystalline resins, and more specifically, as toner resins semicrystalline polyolefin polymers with a melting point of from about 50.degree. to about 100.degree. C., and preferably from about 60.degree. to about 80.degree. C. of, for example, the following formulas wherein X is a number of from about 250 to about 21,000; the number average molecular weight is from about 17,500 to about 1,500,000 as determined by GPC and the M.sub.w /M.sub.n dispersity ratio is from about 2 to about 15.
I. Polypentenes-(C.sub.5 H.sub.10).sub.X PA0 II. Polytetradecene-(C.sub.14 H.sub.28).sub.X.
In a patentability search report, the following United States patents are recited: U.S. Pat. No. 4,217,406, which relates to a process for the preparation of toner compositions by melt-kneading a crosslinkable functional group containing resin and a colorant with a polyfunctional resin capable of reacting with the crosslinkable group containing resin, or a low molecular weight crosslinking agent, and wherein acrylic copolymer with styrene and polyester resins are selected; U.S. Pat. No. 4,824,750, which relates to a toner comprised of certain crosslinked styrene copolymers with an insoluble gel content of from about 20 to about 60 percent; and as background interest U.S. Pat. Nos. 3,941,898; 4,617,249; 4,894,309 and 4,954,408. This prior art appears to be specific to acrylates and polyesters, which are activated to crosslinking by addition and condensation reactions generally accomplished during copolymerization reactions.
While investigating crosslinking reactions with styrene-butadiene copolymers subsequent to polymerization it was found that the stereo-chemistry of butadiene incorporation in the copolymer is crucial to the formation of crosslinks and to improved toner properties. In general, polymerized 1,2-butadienyl groups are activated to crosslinking, whereas polymerized 1,4-butadienyl groups are inactive to crosslinking unless drastic reaction conditions are used, typically greater than 200.degree. C.
U.S. Pat. Nos. 3,941,898 and 4,824,750 relate to the preparation of crosslinked toner resins obtained by crosslinking the resin during the polymerization reaction by inclusion of suitable difunctional monomeric and oligomeric crosslinking agents. Suitable crosslinking agents include aromatic divinyl compounds, diacids, and diacrylates. The methods taught are applicable to polyacrylates and polyesters. Butadiene and butadiene containing polymers do not appear to be mentioned in, for example, the lengthy lists of acceptable vinyl and divinyl containing materials suited to the patent's teachings, including most commonly, divinyl benzene.
U.S. Pat. No. 4,217,406 relates to a process for preparing crosslinked toner by melt kneading a reactive resin with a suitable crosslinking agent, usually a multifunctional oligomer. The teachings are specific to acrylic copolymers and polyester resins with butadiene and butadiene containing polymers being absent from a lengthy list of acceptable reactive monomers, multifunctional monomers and oligomers suitable as crosslinking agents.
One explanation for the omission of butadiene, and specifically, styrene-butadiene copolymers in the teachings of U.S. Pat. Nos. 4,217,406 and 3,941,898 is that styrene-1,4-(cis- and trans-)butadiene copolymers readily available from the free radical copolymerization of styrene with butadiene are not readily crosslinked under the melt or copolymerization reaction conditions described. We have not been able to crosslink styrene-1,4-butadiene copolymers with benzoyl peroxide under mild melt mixing conditions used to prepare toners, for example 150.degree. C., for 30 minutes using a Brabender melt mixer. Moreover, soluble, uncrosslinked styrene-1,4-butadiene copolymers are the chief product obtained when styrene and butadiene copolymers are copolymerized with free radical catalysts. Clearly, butadiene is not acting as a difunctional crosslinking agent under these conditions and the olefinic double bonds produced are not reactive towards radicals generated by benzoyl peroxide and the like. When either acrylate or ester difunctional crosslinking agents are used with styrene-1,4-butadiene copolymers, homopolymerization of polyacrylates or polyesters are preferred. Moreover, reactivity ratios prominently disfavor crosslinking and co-reaction of esters and acrylates with styrene-1,4-butadiene copolymers under conditions taught in U.S. Pat. No. 3,941,898. Consequently, styrene-butadiene resins do not appear to be interchangeable with acrylate and ester resins.
U.S. Pat. No. 4,824,750 relates to toners with fusible, crosslinked binder polymer. A list of suitable crosslinking compounds begins at line 62, page 7, of the '750 patent, and a lengthy list of acceptable materials excludes butadiene and butadiene-containing copolymers. However, Table 1, part E, on pages 11 and 12, lists an ethylenic unsaturation site such as butadiene, for example, poly(styrene-co-methyl methacrylate-co-ethylhexyl methacrylate-co-butadiene) along with E-1, a curing agent consisting of elemental sulfur admixed with a sulfur containing compound such as mercaptobenzothiazole. This polymer incorporates butadiene as the 1,4-regio-stereo-isomer, and the curing agent described is similar to one used for the vulcanization of tire rubber made with poly-cis and trans-1,4-butadiene. The curing conditions required are much more severe than those typically used to process toners. Moreover, the examples cited in the '750 patent are specific to polyacrylate and polyester resins in which crosslinking takes place during copolymer preparation and not subsequently after the polymer had been made. The reaction conditions and peroxide used in the preparation of the resin are inadequate to crosslink the resin, otherwise crosslinking of the olefinic groups would occur during the copolymerization reaction and would lead to polymer insolubility and resistance to flow with heat.
Surprisingly, it has been determined that styrene-1,2-vinylbutadiene copolymers prepared by anionic copolymerization can subsequently be crosslinked with heat (&gt;140.degree. C.) and with free radicals (thermally generated from benzoyl peroxide and azobisisobutyronitrile) using a melt mixing apparatus in the absence of difunctional crosslinking agents. This result is contrary to that obtained with styrene-1,4-(cis-and trans-)butadiene copolymers which are stable to heat and peroxides. Apparently the 1,2-vinyl-butadienyl is more active than the cis- and trans-1,4-butadienyl conformer towards crosslinking reactions. The presence of a suitable crosslinking agent such as a difunctional monomer or oligomer is unnecessary because the 1,2-vinyl groups undergo addition and combination reactions with each other. Thus, the crosslinking reaction is simplified, and polymer homogeneity in the crosslinked product is not affected. One explanation why the crosslinkable, styrene-1,2-vinylbutadiene copolymers have not been reported is because these resins are unique to the anionic polymerization process and heretofore have not been commercially available.
Although the above described toner compositions and resins in prior art patents are suitable for their intended purposes, in most instances there continues to be a need for toner and developer compositions containing new resins, especially toner resins suited to black and color prints and transparencies. More specifically, there is a need for toners which can be fused at lower energies than many of the presently available resins selected for toners. There is also a need for resins that can be selected for toner compositions which are of low cost, nontoxic, nonblocking at temperatures of less than 50.degree. C., jettable, melt fusible with a broad fusing latitude, cohesive above the melting temperature, and triboelectrically chargeable. In addition, there remains a need for toner compositions which can be fused at low temperatures, that is for example 25.degree. C. (50.degree. F.) or less, as compared to those presently in commercial use which require fusing temperatures of 300.degree. to 325.degree. F., thereby enabling with the compositions of the present invention the utilization of lower fusing temperatures, and lower fusing energies permitting less power consumption during fusing, and allowing the fuser system particularly the fuser roll selected, to possess extended lifetimes. Another need resides in the provision of developer compositions comprised of the toner compositions illustrated herein, and carrier particles. There also remains a need for toner and developer compositions containing additives therein, for example charge enhancing components, thereby providing positively or negatively charged toner compositions. Furthermore, there is a need for toner and developer compositions with polymers prepared by reactive extrusion methods, reference copending application U.S. Ser. No. 07/814,641 and U.S. Pat. No. 5,227,460, the disclosures of which are totally incorporated herein by reference, that will enable the generation of solid image area with substantially no background deposits, and full gray scale production of half tone images in electrophotographic systems.
There is also a need for novel polymers, and mixtures of the aforementioned polymers and with T.sub.g-mid of from about 26.degree. to about 60.degree. C., and preferably from about 40.degree. to about 58.degree. C., and wherein toner compositions containing the aforementioned resins can be formulated into developer compositions which are useful in electrophotographic imaging and printing systems, and wherein fusing can, for example, be accomplished by heated rolls, flash, radiant with heated ovens, and cold pressure fixing methods.